Quick setting mortars, emulsion miscible polymer cement mortars and polymer mortars are well known materials for use in repairing structures. Quick setting mortars are characterized by a shorter set time and are prepared by adding alkaline set accelerating agents, primarily of calcium aluminate, alkali metal aluminates, alkali metal carbonates, etc., to a dry or wet mortar mix. However, in almost all cases, the added components have a smaller bond strength than the cement itself and their durability is also poor. Polymer cement mortars exhibit strong adhesion to structural bodies on account of the incorporated resins but since they harden very slowly, satisfactory adhesion to structural bodies cannot be achieved if high strength is required within a short period of time or if water is oozing out of the substrate. Materials based on polymer mortars are not only adjustable in hardening time but they also exhibit strong adhesion to structural bodies. However, many of those materials fail to adhere to wet surfaces and even if they can be bonded to wet surfaces, they have to be applied by troweling which does not have high operational efficiency per unit time.
Unlike such repair materials, cements having both aggregates and set accelerating acrylates or methacrylates can harden within very short times of one minute or less, even if they are applied to structures containing much free water, and, of course, harden quickly on ordinary structures, and develop high strength after hardening. A repair material made of such a composition was first disclosed in JP-A-61-117148 (the term "JP-A-" as used herein means an "unexamined published Japanese patent application") and is now in common use.
While repair materials of this type can be applied by various methods, two common approaches are described in JP-A-58-27992, JP-A-57-209366 and JP-A-58-143098. One method is a wet process in which a covering material composed of cement and aggregates is mixed with water to form a liquid mixture (slurry) which is combined with an aqueous solution of the set accelerating agent in a spray nozzle, from which the combined material is sprayed; and the other method is a dry process in which a powder mixture consisting of the covering material (cement plus aggregates) and the set accelerating agent is combined with water in a spray nozzle from which the combined material is sprayed.
In the wet method of applying repair materials that use acrylates or methacrylates (which are hereafter collectively referred to as (meth)acrylates), an aqueous solution of (meth)acrylates is added to cement and aggregates or a mixture thereof with water and the resulting blend is sprayed by means of a conventional spray system and nozzle. This conventional method, however, has various problems. For example, the blend when sprayed onto a wall can "rebound" excessively from the wall surface. Also, scale may be deposited in an high amount on the interior sides of the nozzle. Since the removal of deposited scale is time-consuming, the operational efficiency of this wet process may not be high. Further, the spray nozzle can be easily clogged by the scale.
There are also problems associated with the inherent nature of the work of repairing deteriorated or damaged structures, i.e., often insufficient time is allowed for such repair work. As is typical in the case of repairing railroad tunnels, the work must be started by turning off the electric power after the last train for the day and it must be completed before the power is turned on the next morning, and it is essential that the necessary strength of the repair material be developed by the time the first train comes. Such limitations also apply to jobs such as protecting the face of slopes, and the job must be completed within a predetermined time period as is often the case for protecting the sloping faces of dams. Under these circumstances, there has developed a great demand for a spray method that can be completed within a short time, that insures strong adhesion to structural bodies within a very short time and that enables structures to be protected and reinforced within a short time. However, the existing methods are not always capable of achieving repair over a satisfactory area per unit time and, in addition, considerable time is often required for the development of the desired strength.